J. Med. Chem. (1999), 42 (4), 730-741 discloses 6-phenyl-N-[1-(phenylmethyl)-4-piperidinyl]-3-pyridazinamine and analogous compounds as acetylcholinesterase inhibitors.
Farmaco, Vol. 35, no. 11, 1980, pages 951-964 discloses substituted N-[4-piperidinyl]-2-aminopyrimidines having dopaminergic activity, i.e. most of the disclosed compounds are agonists at the dopamine D2 receptor. Since none of the compounds tested antagonized the stereotyped behavior induced by a subsequent dose of apomorphine they may also be considered to be devoid of dopamine receptor blocking properties. The compounds of the present invention differ in the presence of a pyridazine instead of a pyrimidine and the unexpected finding that they exert an antagonistic effect at the dopamine D2 receptor.